Blue whales are rorquals (family Balaenopteridae), a family that includes the humpback whale, the fin whale, Bryde's whale, the sei whale, and the minke whale. The family Balaenopteridae is believed to have diverged from the other families of the suborder Mysticeti as long ago as the middle Oligocene (28 Ma ago). The blue whale lineage diverged from the other rorquals during the Miocene, between 7. 5 and 10. 5 million years ago. However, gene flow between the species appears to have continued beyond that date. The blue whale has the greatest genetic diversity of any baleen whale, and a higher than average diversity among mammals. The earliest known anatomically modern blue whale is a partial skull fossil found in southern Italy, dating to between 1. 25 and 1. 49 million years ago. The whale is estimated to have been between 23. 4 and 26. 1 meters (76. 8 to 85. 6 ft) long in life. This finding overturns a previous hypothesis that baleen whales rapidly reached their modern sizes at 300,000 years ago, with the most likely date being a more gradual change around 3. 6 million years ago, possibly earlier.
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